netdev - Re: [RFC PATCH 0/2] selinux: avoid nf hooks overhead when not needed

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Date:	Wed, 6 Apr 2016 19:15:23 -0400
From:	Paul Moore <paul@...l-moore.com>
To:	Florian Westphal <fw@...len.de>
Cc:	Paolo Abeni <pabeni@...hat.com>,
	linux-security-module@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	James Morris <james.l.morris@...cle.com>,
	Andreas Gruenbacher <agruenba@...hat.com>,
	Stephen Smalley <sds@...ho.nsa.gov>, netdev@...r.kernel.org,
	selinux@...ho.nsa.gov
Subject: Re: [RFC PATCH 0/2] selinux: avoid nf hooks overhead when not needed

On Wed, Apr 6, 2016 at 6:14 PM, Florian Westphal <fw@...len.de> wrote:
> netfilter hooks are per namespace -- so there is hook unregister when
> netns is destroyed.

Looking around, I see the global and per-namespace registration
functions (nf_register_hook and nf_register_net_hook, respectively),
but I'm looking to see if/how newly created namespace inherit
netfilter hooks from the init network namespace ... if you can create
a network namespace and dodge the SELinux hooks, that isn't a good
thing from a SELinux point of view, although it might be a plus
depending on where you view Paolo's original patches ;)

> Do you think it makes sense to rework the patch to delay registering
> of the netfiler hooks until the system is in a state where they're
> needed, without the 'unregister' aspect?

I would need to see the patch to say for certain, but in principle
that seems perfectly reasonable and I think would satisfy both the
netdev and SELinux camps - good suggestion.  My main goal is to drop
the selinux_nf_ip_init() entirely so it can't be used as a ROP gadget.

We might even be able to trim the secmark_active and peerlbl_active
checks in the SELinux netfilter hooks (an earlier attempt at
optimization; contrary to popular belief, I do care about SELinux
performance), although that would mean that enabling the network
access controls would be one way ... I guess you can disregard that
last bit, I'm thinking aloud again.

> Ideally this would even be per netns -- in perfect world we would
> be able to make it so that a new netns are created with an empty
> hook list.

In general SELinux doesn't care about namespaces, for reasons that are
sorta beyond the scope of this conversation, so I would like to stick
to a all or nothing approach to enabling the SELinux netfilter hooks
across namespaces.  Perhaps we can revisit this at a later time, but
let's keep it simple right now.

-- 
paul moore
www.paul-moore.com